Unique physical properties and an abundant supply have established asphalt as a major raw material for use in industrial applications which involve structural adhesives and waterproof protective films. The major markets for these industrial applications are road paving and roofing, respectively. Although these two markets have final products that are physically quite different, certain basic similarities do exist. For instance, both asphalt cement and mineral filled roofing asphalt can consist of the combination of asphalt with silica- or limestone-based minerals. Consequently, chemical and physical factors which can influence the asphaltic coating of minerals are operative in both applications.
Residual oils and/or bituminous materials, such as aphalt, used in the preparation of pavements do not coat and adhere well to mineral aggregates unless the aggregate is substantially dry, and, for this reason, in conventional pavements it may be necessary to dry the mineral aggregate prior to blending with the bituminous material.
Mineral aggregates employed in road pavements range in character from hydrophilic to hydrophobic. In general, siliceous and acidic minerals, such as sands and gravels, tend to be hydrophilic while calcareous, alkaline minerals, such as limestone, tend to be more hydrophobic. It has been observed that the mineral aggregates appear to have a greater attraction for water than for oil or bitumens and that it is difficult to obtain complete or satisfactory coating of aggregates by oil or bitumen when water is present. Furthermore, even though satisfactory coating may be obtained by using dry aggregates, the oil or bitumen tends to be displaced if water enters the pavement or road after paving is completed. Compounding these problems is the decrease in the supply of high quality aggregates coupled with the increasing variability of paving asphalts.
One approach which has been used to decrease the severity of the problems attributed to poor adhesion between the aggregate and bitumen and/or stripping of the bitumen from the aggregate due to the presence of moisture has been to include an additive (hereinafter referred to as an antistripping agent) in the bitumen prior to combination with the aggregate. The antistripping agents serve to enhance the coating of the aggregate by bitumens and retard displacement of the aggregate-bitumen bond by water.
The art discloses several antistripping agents which are useful as additives in bitumens and asphalts. For example, U.S. Pat. No. 2,361,488 to L. A. Mikeska, which is hereby incorporated by reference, discloses antistripping agents having the general formula: ##STR1## wherein R is either a saturated or unsaturated alkyl group ranging from 10 to 23 carbon atoms.
U.S. Pat. No. 2,386,867 to J. M. Johnson, which is hereby incorporated by reference, discloses antistripping agents which comprise (1) an acylated polyamine in which at least one amino nitrogen has been converted into an amide group by reaction with a high molecular weight carboxylic acid and in which at least one amino nitrogen has been reacted with a high molecular weight carboxylic acid to form an amine soap and (2) an acylated polyamine in which at least two amino nitrogens have been reacted with high molecular weight carboxylic acid to form amine soaps.
U.S. Pat. No. 2,438,318 to J. M. Johnson, which is hereby incorporated by reference, discloses compositions useful as antistripping agents which are salts of acylamidoamines containing at least one free amine group with a freely water soluble acid, the acyl group in the amidoamine being the acyl group of a higher fatty acid and the amine group which is reacted with the water soluble acid (to form the salt) being unsubstituted.
Another method used to prevent moisture damage in paving materials is to include specific mineral fillers in the aggregate. The most common fillers are those which are easily hydrated and include calcium hydroxide, Portland cement or combinations thereof.
Despite the use of the above-described organic or inorganic additives, certain paving materials remain susceptible to moisture damage such that additional improvement is desirable.